David wrote:
"In addition to coms between the sheds and house, there are links
between sheds (hence require omni-directional)."

The benefit of simple and directional 915 MHz antennas is so significant
that you might consider making one site a repeater and all other sites
directional, communicating through the repeater. A small antenna can
have much gain at 915 MHz. You could conveniently use full-duplex (2
frequencies) for simplicity..

Best regards, Richard Harrison, KB5WZI